Despite these advances, future research is important to understand better the details of this galaxy population and to connect it with galaxies in the Epoch of Reionization.
While the above results contribute to our understanding of relatively massive and mature main-sequence galaxies, conclusions about the fainter end of the population cannot be made with the current sample. Extending the sample to lower stellar masses and (likely) less mature galaxies (in terms of chemical enrichment) would provide an important comparison. For example, does the C\(^+\)\(-\) SFR relations still hold for such galaxies? Is star formation more dominated by cold gas accretion or mergers in fainter galaxies?
A large sample of lensed galaxies at \(z=\)  4–6 would serve as a promising avenue to answer such questions. With enough magnification, ALMA observations of the low-mass end of the main-sequence would not require significantly more time.
ALPINE builds a basis sample at this epoch, which can serve as “anchor” for other studies at lower and higher redshifts. An important study to mention in this context is REBELS, a high-redshift extension of ALPINE to measure C\(^+\)  and far-IR continuum at \(z>6.5\)  using a spectral scan of galaxies with photometric redshifts [1]}. A careful comparison between REBELS and ALPINE would inform us about possible different galaxy evolution in the Epoch of Reionization as well as shortly thereafter (see, e.g., [2]}).
In addition to existing surveys, a higher-resolution C\(^+\)  and dust-continuum follow-up with ALMA would further help us understand this important epoch in galaxy evolution. Sub-kpc resolution observations would reveal the location of star-formation as well as their gas velocity dispersion. The comparison to studies at lower redshifts [3]} would help us constrain star formation in general as well as the role of feedback from stellar winds, SNe, and AGN on smaller spatial scales than currently possible.
The combination of deep high-resolution and shallow low-resolution observations with ALMA would also significantly improve the measurement of velocity curves to pin down the dark matter content of these galaxies. The spatial sampling of current observations is not fine enough to unambiguously determine between a flat or declining velocity curve out to large radii [4]}.
Finally, JWST will be the workhorse for optical exploration of the galaxies, by providing, for example, resolved metallicity measurements or stellar mass and optical dust maps. The paper by [5]} already provides a taste of the possibilities that arise by combining optical emission lines with UV and sub-mm measurements.
